Apparatus and method for combustion

ABSTRACT

To enable a burnpot for a corn burning stove to be continuously operated, the burnpot has an openable bottom with at least a first and second position, one of said at least fist and second positions being substantially closed to enable a body of combustible fuel to burn on its upper surface, the other of said at least first and second positions providing an opening, burnpot side wall portions and a top of said burnpot being shaped so as to permit a solid clinker to drop out of the opening in the openable bottom when the openable bottom is in its second position. A combustion volume is provided between said openable bottom, said side surfaces and said top, said combustion volume having an upper portion and a lower portion whereby a fire on a combustion surface in said lower portion burns upwardly toward said upper portion so that byproducts of combustion build on the combustion surface to cause burning fuel to burn at a higher level; said higher level having a smaller cross sectional area than said lower portion whereby the byproducts of combustion may drop as a unit out of said opening. A combustion retention openable burnpot bottom to retain combustion in the burnpot when byproduct of combustion is removed through the openable bottom.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for combustion and moreparticularly to a combustion technique and equipment including a burnpotsystem and a method of operating the burnpot system.

It is known to provide a combustion system for removing ash convenientlyfrom the bottom of a burnpot and to provide air from the bottom of theburnpot or near the bottom. The prior art systems generally have: (1)top sections larger than their bottom sections so as to be generallyfunnel shaped; and (2) bottom working surfaces that are permanentlymounted and either solid or with gratings that have small openings toremove some ash.

This type of burnpot has several disadvantages, such as for example: (1)in operation, they must be extinguished to clean and then be restartedor have the byproducts of combustion such as ash removed little bylittle with the burning coals remaining at substantially the sameelevation; (2) they are limited to certain fuels that burn almostcompletely or must frequently be extinguished to remove large clinkersor coals; and (3) the removal and disposal of coals is a difficultoperation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a novel burner,such as for example a stove or furnace.

It is a further object of the invention to provide a novel method forcombustion.

It is a still further object of the invention to provide a novel burnpotfor use in a burner.

It is a still further object of the invention to provide a burnpot intechnique which is designed for the easy removal of large solidclinkers.

It is a still further object of the invention to provide a novel burnpotand a technique for the continuous burning of fuel even during theremoval of clinkers.

It is a still further object of the invention to provide a novel burnerof a type adapted for biomass which forms relatively large solidclinkers.

It is a still further object of the invention to provide a novel cornburner.

In accordance with the above and further objects of the invention, anovel burnpot has an openable bottom with at least first and secondpositions. One of the first and second positions is a substantiallyclosed position that enables a body of combustible fuel to burn on itsupper surface. The other of said at least first and second positionsprovides an opening. The burnpot sidewall portions of the burnpot and atop portion of a burnpot are shaped to permit a solid clinker to dropout of the opening in the openable bottom when the openable bottom is inits second position.

The openable bottom may be constructed in any manner that provides aclosed position to support combustion and an open position to permit alarge solid clinker to drop out of the burnpot. Thus, it may be hingedand latched at one end, it may slide in and out, it may be held bycatches around each end so to be capable of being completely removed, orany other arrangement may be utilized.

In the preferred embodiment, the sides are shaped as an inverted funnelto be smaller at the top where fuel may be deposited through the opentop and larger at the bottom so it can open and remove a large clinkersuch as the type normally formed in corn burning stoves and furnaces.

A combustion retention slide is positioned to be moved into the burnpotclose to the surface of the burning fuel. If above the coals, new fuelmay be applied on top of the combustion retention slide and the firebeneath the combustion retention slide will ignite the new fuel. Theopenable bottom can then be opened and the ash removed. When the ash isremoved, the openable bottom may be closed and the slide retracted sothat there will be fire at the bottom again without reigniting thestove. In another embodiment, the slide may be pushed just beneath theburning surface of combustion and then the openable bottom opened toremove the byproducts underneath the burning portion. The openablebottom may then be closed and the slide removed to drop burning fuel tothe bottom.

While the bottom is large enough to remove a solid clinker such as thetype commonly formed in corn stoves, it cannot be so large thatcombustion cannot be supported when the burning fuel is dropped fromabove the combustion retention slide to the bottom. Moreover, inembodiments in which fuel is poured through the smaller top, thedifference in cross sectional area between the top and bottom cannot beso great as to not permit fuel to be spread over a sufficient area ofthe bottom to maintain combustion.

At start up and during operation when the temperature settings arechanged or the rate of burning is changed to accommodate increased heatdemand or decreased heat demand, the control system moves from fuel feedsetting to fuel feed setting in a controlled serial sequence with adelay time being provided between settings to avoid a rapid change inrates of fuel feed. The delay enables the fire to build up slowly to alarger fire each time fuel is added before additional fuel is added.Thus, the fire is not smothered with fuel. This is done without stirringthe coal bed because stirring the coal bed results in a reduction inefficiency.

From the above description, it can be understood that the burnpot of theinvention and stoves that accommodate it have several advantages, suchas: (1) a continuous flame may be maintained while byproducts of burningare removed; (2) solid clinkers may be easily removed from the bottom;and (3) the stoves containing this burnpot are convenient for the user.

BRIEF DESCRIPTION OF THE DRAWINGS

The above noted and other features of the invention will be betterunderstood from the following detailed description when considered withrespect to the following drawings in which:

FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is simplified fragmentary side view of the stove of FIG. 1 inaccordance with an embodiment of the invention;

FIG. 3 is another simplified fragmentary side view of the stove of FIG.1 in accordance with an embodiment of the invention;

FIG. 4 is a plan view of a burnpot in accordance with an embodiment ofthe invention;

FIG. 5 is an elevational front view of the embodiment of FIG. 4

FIG. 6 is an elevational side view of the embodiment of FIG. 4;

FIG. 7 is a simplified side view of a firebox useful in the embodimentof FIG. 1;

FIG. 8 is a plan view of an openable bottom of the burnpot of FIGS. 4-6in accordance with an embodiment of the invention;

FIG. 9 is a side view of the openable bottom of FIG. 8 in accordancewith an embodiment of the invention;

FIG. 10 is an elevational front view of the openable bottom of FIG. 8 inaccordance with an embodiment of the invention;

FIG. 11 is a plan view of a combustion retention slide in accordancewith an embodiment of the invention;

FIG. 12 is a front elevational view of the combustion retention slide inaccordance with the embodiment of FIG. 11;

FIG. 13 is a side view of the combustion retention slide of FIG. 11 inaccordance with an embodiment of the invention;

FIG. 14 is a side view of a heat exchanger tube scraper in accordancewith an embodiment of the invention;

FIG. 15 is a plan view of the heat exchanger tube scraper of FIG. 14 inaccordance with an embodiment of the invention;

FIG. 16 is a block flow diagram illustrating the steps used in cycling acorn stove in accordance with an embodiment of the invention;

FIG. 17 is a simplified block diagram of an ignition control system inaccordance with an embodiment of the invention; and

FIG. 18 is a block diagram of the process of igniting the stove of FIG.1 in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

In FIG. 1, there is shown a perspective view of a burner 10, which maybe for example a stove or furnace, having an enclosure 14, with anaccess door 12, an ash pan 16, a rod 20, a rod 22, a heat exchanger tubescraper rod 24 and a fuel hopper lid 18. The access door 12 has atransparent window through which a fire box can be seen having within ita burnpot chamber, burnpot, feeder system, exhaust system, heatexchanger system and combustible air intake system, none of which areshown in FIG. 1. The fuel hopper in the preferred embodiment includesthe hinged lid 18 in the top of the enclosure 14 exposing an openingthrough which fuel, such as for example corn can be poured. To permitoperation of the stove or furnace 10 from outside the enclosure 14, therod 20 is connected to an openable bottom of a burnpot (not shown inFIG. 1), the rod 22 is connected to a combustion retention slide (notshown in FIG. 1), and the heat exchanger tube scraper rod 24 isconnected to a heat-exchanger scraper (not shown in FIG. 1)

For convenience in operating the burner 10 from outside of the enclosure14, the rods 20, 22, and 24 extend from the front of the enclosure 14and may be used in the preferred embodiment to manually actuateoperations within the enclosure by moving the rod. The openable burnpotbottom rod 20 permits the openable bottom of the burnpot to be opened toremove clinkers from the bottom of the burnpot. The combustion retentionslide rod 22 permits the combustion retention slide either: (1) to bemoved under the surface of the burning fuel; or (2) to be moved to alocation just above the burning fuel and close enough to cause burningfuel poured onto the combustion retention slide to be ignited. If thecombustion retention slide is moved just below the burning fuel, itserves to hold the burning fuel in the burnpot while a clinker is beingremoved. If it is moved to a location just above the burning fuel andsufficiently close to the burning fuel so that new fuel can be ignitedabove the combustion retention slide, it retains the new fire until theclinker is removed. After the clinker is removed, the combustionretention slide can be removed from the opening in the burnpot to permitthe burning fuel to drop to the bottom of the burnpot. This enables afire to burn while the clinker is removed from the burnpot by openingthe openable bottom of the burnpot (not shown in FIG. 1).

In FIG. 2, there is shown a burner 10 such as a stove or furnace orincinerator having a burnpot 26, a burnpot seat 28, the ash pan 16, acombustible air system 48, a convection air system 54, and a fuel feedsystem 56. With this arrangement, combustible air flows through theburnpot 26 around tubes of heat exchangers and the heated gaseousbyproducts of combustion and excess air flows out of exhaust tubing. Atthe same time, convection air flows through the inside of the tubes ofthe heat exchanger and into the area to be heated. Of course, thecombustible air or gaseous byproducts of burning could flow through thetubes of the heat exchanger and convection air around the tubes.

The burnpot 26 rests on a burnpot seat 28 having an opening with aflange that supports the burnpot 26 while leaving room for clinkers tofall through the burnpot when its openable bottom is removed to dropinto the ash pan 16. The burnpot 26 has the opening bottom 28, side wallportions with apertures 72, an open top 34 and a combustion retentionslide 86 (not numbered in this FIG. 2; see FIGS. 11, 12 and 13). It iswithin a burnpot compartment 30 which confines the combustible air sothat it flows into the burnpot 26 to support combustion and rises aboveit to flow to the heat exchanger tubes and from there out the exhausttubing which may exhaust into the atmosphere outside of an enclosurecontaining the burner 10.

The combustion retention slide is positioned above the openable bottomat a location where the fire burning from the openable bottom upwardlywill rise on the byproducts of burning to a level just beneath thelocation of the slide when it is moved into the burnpot. In thislocation, new fuel may be applied on top of the combustion retentionslide 86. At this location, the fuel resting on top of the combustionretention slide is ignited by the fire beneath it. After this hashappened, the openable bottom may be opened, such as by removing it fromthe bottom of the burnpan, to permit the byproducts of combustion todrop into the ash pan 16. In the alternative, if the byproducts ofcombustion lift the burning coals (typically corn or other biomass)above the location for the combustion retention slide 86, the slide maybe forced just below the burning coals so as to support them. Theopenable bottom may then be removed so that the clinker dropsdownwardly. In both cases when the combustion retention slide is pulledoutside of the burnpot or to one side, the burning combustion will dropto the bottom.

The burnpot itself is shaped in the matter of an inverted truncatedfunnel with a smaller opening at the top and an openable bottom. Theremay be straight portions or other portions but the outward slantingwalls must slant far enough outward between the top and the bottom sothat the clinker will pull free against the resistance of the sidewalls. In this specification we would define the shape of the burnpot asa generally truncated, inverted-funnel shape, with the understandingthat this would encompass many geometries such as an inverted truncatedcone or a truncated pyramid with a truncated top that is smaller thanthe operable bottom. To be operable, it is necessary for the clinker,which in the case of a corn burning stove will frequently be one solidmass of byproducts of combustion, to drop out of the bottom rather thansticking to the sides as would be the case generally with vertical wallsor funnel shaped walls with a smaller bottom than top.

The combustible air system 48 in FIG. 2 includes the exhaust blower 78,a heat exchanger system 38 and outlet pipes 88 to permit exhaust to flowout of a housing for the stove and inhabitants into the outsideatmosphere. The heat exchanger system 38 includes an upper heatexchanger 40 generally positioned horizontally and a back heat exchanger44 generally positioned vertically. With this arrangement thecombustible air follows a flow path from the inlet 80A in the directionof the arrows to 80B downwardly to 80C where it passes into the openablebottom 52 of the burnpot 26 and through the apertures 72 in the sidewall portions of the burnpot 26 to support combustion therein and thenupwardly as shown at 80D around the heat exchanger top pipes 36 of heatexchanger 40 as shown at 80E and 80F and from there downwardly as shownat 80G through the side heat exchangers 44 and to the exhaust blower 78following the path shown at 80H and 80I to the exhaust pipes 80J, 80K,and 80L for exiting into the atmosphere through the exhaust outlet pipesshown schematically at 88. Similarly, the convection air system 54includes a convection air blower 90 which draws convection air through aflow path including the air inlet shown by the arrow 92A through thetubing following the path shown at 92B upwardly around side heatexchanger pipes 44 as shown at 92C upwardly through the upper heatexchanger pipes 40 as shown at 92D, 92E, 92F, 92G and 92H into the spacethat is to be heated by the stove 10.

Because the byproducts of combustion accumulate on the heat exchangertubes 36, a heat exchanger tube scraper 94 (not shown in FIG. 2) ismounted to be moved across the heat exchanger tubes 36 when the heatexchanger tube scraper rod 24 is moved from outside of the stoveenclosure 14. In this manner the heat exchanger tubes 36 can be keptrelatively clean and the space between them sufficiently clear to permitefficient heat exchange to the convection air through the inside of thetubes.

In FIG. 3, there is shown a simplified sectional fragmentary view of thefuel feed system 56 within the burner 10 having a fuel hopper lid 18, afuel hopper 32, an auger system 98, a fuel guide 102, drop tube 100.With this arrangement, fuel hopper 32 is dropped to the auger system 98which moves it upwardly into the drop tube 100. From the drop tube 100it falls to the fuel guide 102 which guides it to the opening top 34 ofthe burnpot 26. The fuel hopper 32 is sized in accordance with the speedof the auger 98 so as to move fuel into the drop tube 100 forapplication by the guide 102 to the burnpot at a rate for efficientburning at different heat settings to avoid blocking of air to theburning coals. The amount of fuel in the fuel hopper and the feed ratemay be preselected for fixed periods of time such as 24 hours so thatthe ash pan can be emptied, the ash dropped down from the burnpot bypulling the openable bottom and fuel added at each convenient period,which may be 24 hours or perhaps twice a day, once late at night andagain early in the morning as preselected by the user.

While a stove particularly adapted for the burning of biomass isillustrated in FIGS. 1-3, any combustion device may utilize the novelburnpot of this invention. Moreover, while a specific fuel feedingsystem is described, there are many such variations in feed systems, anyof which can be employed with the proper combustion system. In thespecific system of FIGS. 1-3, the bottom of the burnpot is openable. Inthe preferred embodiment, it may slide completely free of the burnpot sothat a large clinker or fused mass of already burnt coals may be droppedthrough the bottom. The burnpot is shaped to expedite this process.However, the openable bottom may take on different configurations. Itmay be slide mounted within a bottom panel or it may be hinged to openand drop down or it may be one that is held in place by detents whichcan be removed to permit the dropping down of the bottom into the ashpan. Any of these configurations are workable.

The openable bottom performs two functions. One of the functions is tohold the ash until it is desirable to move the ash while stillmaintaining combustion above the ash. The other function is to permit anair passageway through the bottom. Preferably, a double walled openablebottom is used in which the top side of the double wall has perforationsso that air may flow into the double box through perforations such as onthe side or through the top portion that doesn't sit entirely below theburnpot but is within the burnpot wrap and upward through perforationsin the top wall. Pulling the box out entirely opens a passageway to thebottom, but when the box is in place, the solid bottom blocks thecombustion air from flowing into the fire box. This function could alsobe performed by two separately removable plates with the bottom platesealing the burnpot compartment and the top plate providing perforationsbeneath the combustion to permit the combustible air to enter theburnpot.

The burnpot is shaped to facilitate the dropping of the clinkers whenthe slide is removed. In the preferred embodiment, that shape has atapered side wall tapering inwardly at higher elevations to have alarger bottom than top. This permits the ready dropping of the clinker.Straight walls at times impede the dropping of the clinker as do funnelshaped walls so that the bottom is smaller than the top.

The side walls of the fire plate are shaped so that the weight of theclinker is sufficient to create a force that overcomes the frictionalattachment to the sides of the burnpot. In the preferred embodiment, thewalls slant outwardly in a manner of an inverted truncated funnel. Thewalls can actually form any configuration such as a slantingparallelopiped as well as a funnel shape or it can be pyramid shaped orany other configuration that permits a relatively easy pulling of ashfree from the walls to permit it to drop into the burnpot. The wallsmust be shaped so that there is sufficient weight of the clinker thatoccurs because of the overall shape of the walls to pull the clinkerpast any portion of the wall to which it tends to stick. The stationaryfrictional force must be less than the weight of the ash that is droppedfrom the top surface of the removable ash to the bottom removable plate.

Although the bottom of the burnpot must be larger than the portions ofthe burnpot above the bottom that will contain the ash, it still must besufficiently small to contain the combustion to an area that maintainsheat sufficient for sustainable combustion. The top and bottom areas aredefined by the need to obtain fuel through the top and at the bottom tobe sufficiently close in size to maintain combustion. Preferably, thewalls should slant outwardly at an angle of between 1 degree to 45degrees from the normal. In the preferred embodiment, the walls areconed shaped and have an angle of six degrees. In FIG. 4, there is showna plan view of the burnpot 26 having the burnpot flange assembly 106,the open top 34 of the burnpot and the rear side 104 of the burnpot,with the interior of the burn pot being visible through its open top 34.The side 104 of the burnpot is positioned flat against one side of theburnpot compartment 30 (FIGS. 1 and 2) and the burnpot flange assembly106 includes the flanges 62A-62C, the upwardly extending wall portions123, 124 and 126 and the angled portion 122. The flanges 62A-62C arepositioned on the other sides to seal the burnpot compartment 30 withthe combustible air system being beneath the burnpot flange assembly 106and the exhaust system being above the burnpot flange assembly 106 sothat the open top 34 of the burnpot 26 that receives fuel and throughwhich byproducts of combustion float is within the exhaust system andare insulated from the combustible air system. The walls 123, 124 and126 extend upwardly to prevent corn from bouncing out of the burnpotwhen moving downwardly from the feed chute that fits against the angledportion 122. A screw can be positioned in the feed chute to scatter thecorn and reduce bounce.

In FIG. 5, there is shown a front view of the burnpot 26 illustratingthe flange assembly 106 and the combustible air portion 118. The burnpotflange assembly 106 includes the side flange members 62A and 62C havingcorresponding ones of the downwardly and outwardly slanting portions110A and 110C and the vertical portions 112A and 112C. These portionsare shaped to intimately contact the inside walls of the burnpotcompartment and seal it so as to maintain combustible air underneath theflange assembly 106 and the exhaust system including the open top 34 ofthe burnpot 26 above the burnpot flange assembly 106.

The flange assembly 106 includes the opening 116 formed as a regularparallelopiped in the preferred embodiment and having the flangeassembly 106 at its bottom end. The flange assembly 106 includes thedownwardly extending flanges 62A and 62C and a vertical outwardlyextending flange 62B on the front that seals the combustible air sectionfrom the exhaust section by lying flat upon a horizontal portion of theburnpot compartment (not shown in FIG. 5). It separates the exhaustportion 116 of the burnpot from the combustible air portion 118 of theburnpot.

The combustible air portion 118 of the burnpot includes the perforatedwalls 108 of the burnpot that angle outwardly so as to permit easierdropping of the coals from the burnpot. The perforations 72 through thissurface or surfaces are sized and angled so as to cause combustible airto flow downwardly into the flame. Near the top portion of theperforated section are a number of slots 120 to receive the combustionretention slide used as described above to sustain combustion while usedcoals from beneath it are being dropped. It is positioned at a levelhigh enough to support the byproducts of combustion and the build upthereof for a convenient period of time, after which the combustionretention slide is moved over the top of the burnpot to sustaincombustion while the coals underneath it are removed. Thus the feedingof fuel, the insertion of the combustion retention slide and the removalof burned ash from the ash pan underneath the fire box are all timed soas to be convenient for the user.

In FIG. 6, there is shown a side view of the burnpot 26 illustrating themanner in which the flange 62C extends outwardly and then slopesdownwardly into the flanges 62A and 62B to form a compartment into whichair may be injected for passage through the openings 72 and use inburning of the fuel.

Generally, in the preferred embodiment, the diameter of the aperturesare 1/16 to ⅜ inch, and they are spaced so that, as the byproducts ofcombustion increase and lift the burning coals and block holes,sufficient air is provided in the burnpot to maintain a rate of burningthat avoids excessive fusing of the fuel to each other. The holes arespaced a minimum of 0.375 inch apart and a maximum of 1.5 inches apart.The fusing of the corn can cause suffocation of the fire and reducedheat. They are drilled so that the internal walls slant downwardly to alevel at which a combustible fire is at some times burning. They pointgenerally downwardly into the location of combustion.

The openings 72 are angled and selected as to size to provide anadequate flow of air to the burning coals. A range of holes between0.0625 inches in diameter and 0.375 inches in diameter have been foundto be suitable. In the preferred embodiment they are spaced in 5 rowsapproximately 0.4 of an inch apart in the horizontal direction andapproximately 6 inches apart in the vertical direction with a top rowthat is closer together. The lower rows are generally equally spaced inthe preferred embodiment in four rows.

While round holes have been selected for convenience in the preferredembodiment the holes may be of any shape. The exact size, spacing,number of holes and shape are selected for maximum effect in sustainingan adequate level of combustion.

In FIG. 7 there is shown a fragmentary simplified side elevational viewof the fire box 128 including the bottom portion of the burnpotcompartment 30 with the burnpot seat 28 within it and at its upper endthe heat exchangers 38. As shown in this view, the burnpot is mountedwithin the fire box 128 in a burnpot seat which adapts to the openablebottom 52 of the burnpot to permit the byproducts of combustion to dropdown into the ash pan. At the top of the fire box 128 is the heatexchanger 38 which receives the exhaust from the burnpot for the purposeof generating heat while the combustible air is contained within theburnpot compartment 30. The burnpot compartment 30 is formed of theburnpot flange assembly 106 resting on top of the burnpot seat 28 toform a compartment which receives combustible air and permits exhaust topass through the compartment from the burnpot. The side 122 is positionagainst the back of the firebox and slots 129 are provided in thebackplate to permit air to enter the burnpot compartment 30 and thusserve as a source of combustible air. In FIG. 8, there is shown a topview of the openable burnpot bottom 52 having a perforated top surface60, a bottom plate 74 (FIG. 9) with openable burnpot bottom wings 62Aand 62B on each side and an upwardly extending flange 64 and an airspacebetween the top surface and bottom plate (FIG. 9). The perforated topsurface 60 contains a number of regularly spaced combustible airapertures serving as a plurality of first openings, two of which areindicated generally at 66 of sufficient size to permit the combustibleair to support a starting combustible bed. The burnpot (not shown inFIG. 8) sits above the openings 66 in the perforated top surface 60 anddoes not overlay the wings 62A and 62B nor the two elongated secondopenings 68A and 68B in the perforated pot. The second openings 68A and68B are between the airspace and the source of combustible air 122 (FIG.7) and are intended to permit combustible air to pass to the bottomsurface of the perforated plate that forms the first bottom wall spacedabove the second bottom wall and then upwardly to the burnpot throughthe first openings extending between the second bottom wall and theinterior of the burnpot, with the plate 74 preventing escape from theburnpot chamber. Thus, the first bottom wall may hold a solid byproductof combustion and include second openings between the airspace and saidsource of combustible air whereby air may pass from the source ofcombustible air and the airspace into the interior of the burnpot. Aninternally threaded nut 76 extends from the upwardly extending flange 64to receive the rod 20 (FIG. 1). Openings may also be present in theright, rear and left sides 70A, 70B and 70C of the openable bottom. InFIG. 9, there is shown a side view of the openable burnpot bottom 52having a first bottom wall with a top surface 60 and a second bottomwall or plate 74 showing the top perforated surface 60, the upwardlyextending flange 64 with the nut 76 welded thereto. As shown in thisview, the flange 64 extends downwardly to a solid plate 74. In thisarrangement, combustible air enters the openings 68A and 68B of theopenable burnpot bottom 52 passes upwardly through the apertures 68A and68B (68B being shown in FIG. 9). Although circular perforations or firstopenings are shown generally at 66 and the two elongated slots or secondopenings at 68A and 68B, any openings that permit the flow ofcombustible air to the bottom of the burnpot will serve the appropriatefunction. Similarly, one slot or a multiplicity of slots could be usedinstead of the apertures 68A and 68B. Any arrangement that permits theflow of air is suitable. To seal the bottom of the burnpot compartment,the wings 62B are shown at the bottom of the double walled openableburnpot bottom but, of course, could be positioned elsewhere since theirfunction is merely to support the double walled bottom and seal thesecond bottom wall 74 which is without substantial openings to the sidesof the burnpot openable bottom against the escape of combustible airwhen the openable bottom is in place closing the bottom of the burnpotwhereby the combustible air is prevented from passing into the firebox.One of the other four sides is sealed against the flange 64 and theother is sealed against a wall of the burnpot chamber with slots toallow combustible air to enter the airspace between the perforated topand the bottom of the openable bottom, whereby air may pass from theairspace into the burnpot. Similarly, as mentioned earlier, theperforated top portion 60 could be a separate sheet metal withperforations and the second bottom portion wall 74 still anotherarrangement with each of them to be removed separately when the ash isto be dropped down. The top perforated surface 60 can be fastened to thesecond bottom wall 74 by any suitable means such as welding orattachment. In the preferred embodiment, it includes downwardlyextending tabs that fit within openings in the bottom plate 74.

In FIG. 10, there is shown a rear elevational view of the openableburnpot bottom 52 showing the upwardly extending flange 64, the nut 76,the top perforated plate 60 and the bottom plate 74 with the wings 62Aand 62B. As shown in this view, the openable burnpot bottom may be movedinto position by the upwardly extending member 64 by grabbing the rod26.

In FIGS. 11, 12 and 13, there is shown a plan view, a front elevationalview, and a side elevational view respectively of a combustion retentionslide 86 having eight fingers 130A-130G of a combustion retention slide86, a bottom retention plate 132, an upwardly extending edge 134, anupwardly extending lip 136 and a nuthole for the combustion retentionslide rod 22. The fingers 130A-130G are formed in the bottom retentionplate 132. The upwardly extending edge 134 is integrally formed with thebottom plate 132, and in the preferred embodiment, extendsperpendicularly thereto with the lip 136 extending from the top edge ofthe lip 134 and having within it the opening 138 for connecting to apull rod 22. With this arrangement, the combustion retention rod mayslide into the burnpot 26 (not shown in FIGS. 11-13) so as to preservecombustion while the byproducts of combustion or the coal beneath it aredropped through the bottom into the ash pan and then removed so as todrop burning coals down to the top surface of the replaced openablebottom of the burnpan so that it is unnecessary to continually reignitethe fire within the burnpot. The combustion retention slide may takemany different forms that provide a support for fuel near the burningcoals beneath it such as a shutter format or partial movable plate orthe like. It is only necessary to hold burning coals while the clinkeris removed from the burnpot and drop them after the clinker is removed.

In FIGS. 14 and 15, there is shown a sectional sideview and a plan viewrespectively of the heat exchanger tube scraper 94 having a base 140, aparallelopiped shaped edge 142 extending outwardly orthogonal to theflat base 140 so as to form a parallelopiped with a rectangular shape,an opening 146 in the edge 142 to receive a nut 148 welded thereto and aplurality of openings 150, each of which corresponds in diameter andlocation to a different one of the heat exchanger tubes. The nut 148receives a pull rod which may be utilized to move the base 140 back andforth over the matching heat exchanger tubes and scrape depositstherefrom.

In FIG. 16, there is shown a block diagram 158 of the normal operationof the burner 10 having a subroutine 160 for igniting the burner andsupplying fuel thereto and a subprocess 162 for removing the spent coalstherefrom while continuing the burning. By continuing the burning, it ismeant that it is unnecessary to extinguish the fire, clean the burnerand restart the fire. The step 164 continues so that this process may berepeated for very long periods of time.

The subprocess 160 for igniting the fire and supplying fuel to it,includes the steps 166 of closing the openable bottom or insuring thatit is closed, the step 168 of igniting the fuel on top of the openablebottom and the step 170 of feeding fuel to the fire as needed.

The subprocess 162 includes the steps 172 of pushing the combustionretention slide either under the coal bed that has reached its level ontop of spent coals or pushing it just above the coals so that it isclose enough to ignite new fuel, the step 174 of forcing the openablebottom sufficiently far open while the coals are still burning to permitremoval of the spent coals while the burning continues above thecombustion retention slide, the step 176 of moving the openable bottomunder the burnpot again to close the bottom and the step 178 of movingthe combustion retention slide from blocking the burnpot to let burningcoals drop to the top of the openable bottom.

In FIG. 17, there is shown a block diagram 180 of a stove ignitionsystem including a printed circuit and microcontroller 182 or othercontrol arrangement, a fuel feed and air control system shown generallyat 186, and an igniter shown generally at 188. The printed circuit andcontrol 182 may include a timer and drivers 131 and 133 or amicroprocessor or any other suitable arrangement. The controller 182communicates electrically with the thermostat 184 so as to maintain aneven temperature in the warmed place, with the fuel feed and aircirculation system 186 and with the igniter 188. With this arrangement,the cycle of feeding fuel, removing ash, providing combustible air andremoving exhaust are controlled. The fuel feed and air control system186 includes a proof of fire detector 190, an air switch 192, a gearmotor drive and auger combination 194, a combustion blower 196, aconvection blower 198 and a manual temperature switch 200. Each of theseunits communicates with the control system 182 to determine when air isto be supplied for combustion, when fuel is to be ignited and the like.

In FIG. 18, there is shown a block diagram 202 illustrating the routinecontrolled by the control system of FIG. 17 for ignition of a fire inthe burner 10 having a startup system 204 and a level by level flow ratesystem 206. The startup system 204 includes the steps 208 of pushing thepower button for combustion air fan and for the convection air fan, thestep 210 of providing a thirty second delay, the step 212 of turning offthe convection fan and moving the combustion fan to setting 1, which isthe lowest setting, the step 213 of starting the feeding of fuel atlevel 1, and the step 214 of waiting to sense the proof of fire switch.With this arrangement, ignition is tried and then the fuel ignited withthe fans going. There is a thirty second delay and then the convectionfan goes off since there is no heat being provided yet and thecombustion fan provides a very low flow of combustion for startup. Thefinal step in this sub-routine is waiting for the proof of fire switchto close.

The subprocess 206 includes the step 216 of sensing proof of fire. Theremay be a series of five minute delays. If fire is detected, the fans andauger are moved to level 2 for five minutes, but if it is not detectedthen the cycle must start again with pushing the power button. At step218, which is level 2, the combustion fan and feed rate increase forfive minutes and then goes to step 220 which is level 3 providing astronger flow of combustion air and more fuel for five minutes and thento step 222 which is level 4 providing a still higher rate of combustionair and another increase in fuel for another five minutes and then step224 which is level 5 for five more minutes. This is the maximum settingfor combustion fan and fuel feed setting, the air flow and fuel feed mayalso be controlled by a thermostat to maintain the temperature in thespace being heated constant. This example shows the sequence of thecontrol board to the maximum level (level 5). During normal operation,the sequence stops at any of the five levels that can be chosen as thedesired level of operation.

Although a preferred embodiment of the invention has been described insome detail, many modifications and variations of the invention, withinthe scope of the appended claims, may be utilized without deviating fromthe invention. Accordingly, the invention may be performed other thanhas been specifically described utilizing the known equivalents in theart as illustrated in the files of the United States Patent andTrademark Office and in the technical literature, without deviating fromthe invention.

1. A burnpot comprising an openable bottom with at least a first andsecond position, one of said at least first and second positions beingsubstantially closed so as to enable a body of combustible fuel to burnon its upper surface, the other of said at least first and secondpositions providing an opening, burnpot side wall portions and a top ofsaid burnpot being shaped so as to permit a solid clinker to drop out ofthe opening in the openable bottom when the openable bottom is in thesecond position; wherein a combustion volume is provided between saidopenable bottom, said side wall portions and said top; said combustionvolume having an upper portion and a lower portion whereby a fire on acombustion surface in said lower portion burns upwardly toward saidupper portion so that byproducts of combustion build on the combustionsurface to cause burning fuel to burn at a higher level; said higherlevel having a smaller cross sectional area than said lower portionwhereby the byproducts of combustion may drop as a unit out of saidopening.
 2. A burnpot within a firebox, said burnpot comprising a sourceof combustion air and an openable bottom with at least a first andsecond position, one of said at least first and second positions beingsubstantially closed so as to enable a body of combustible fuel to burnon its upper surface, the other of said at least first and secondpositions providing an opening, burnpot side wall portions and a top ofsaid burnpot being shaped so as to permit a solid clinker to drop out ofthe opening in the openable bottom when the openable bottom is in thesecond position and a combustion retention openable burnpot bottom toretain combustion in the burnpot when solid byproduct of combustion isremoved through the openable bottom; said combustion retention openableburnpot bottom being located sufficiently close to said openable bottomto cause ignition of fuel on said combustion retention openable burnpotbottom from heat rising from said openable burnpot bottom; said openableburnpot bottom including first and second bottom walls separated fromeach other so as to provide an airspace between the first and secondbottom walls; said first bottom wall having a plurality of firstopenings extending between the second bottom wall and the interior ofthe burnpot, whereby air may pass from the airspace into the burnpot andthe first bottom wall may hold the solid byproduct of combustion and atleast one second opening between the airspace and said source ofcombustible air whereby air may pass from the source of combustible airand the airspace; and said second bottom wall being without substantialopening whereby the combustible air is prevented from passing into thefirebox.
 3. A burnpot comprising an openable bottom with at least afirst and second position, one of said at least first and secondpositions being substantially closed so as to enable a body ofcombustible fuel to bum on its upper surface, the other of said at leastfirst and second positions providing an opening, burnpot side wallportions and a top of said burnpot being shaped so as to permit a solidclinker to drop out of the opening in the openable bottom when theopenable bottom is in the second position wherein said burnpot side wallportions include apertures through them having internal walls, each ofsaid apertures having a corresponding diameter and internal wallthickness; said thickness being equal to the thickness of the side wallportions; said side wall portions slanting downwardly toward theopenable bottom whereby air entering the side wall portions flows withvelocity in the direction of said openable bottom.
 4. A burnpot inaccordance with claim 1 further including a control system having meansfor moving from fuel feed setting to fuel feed setting in a controlledserial sequence.
 5. A burnpot in accordance with claim 4 furtherincluding a delay time between settings to avoid a rapid change in ratesof fuel feed.
 6. A method of operating apparatus comprising the stepsof: permitting fire in a heating apparatus to burn and build up anaccumulation of byproducts of combustion whereby coals burn at a higherand higher level while fuel is added on an openable bottom; closing acombustion retention slide and maintaining burning coals on thecombustion retention slide when the coals have built to a predeterminedlevel; sliding an openable bottom from a closed postion to an openposition to enable a clinker to fall from the bottom while hot coalsremain on the combustion retention slide to enable a body of combustiblefuel to bum on an upper surface of the combustion retention slide,closing the openable bottom; moving the combustion retention slide tocause the burning coals to drop to a top surface of the openable bottom,whereby combustion is supported during removal of the byproducts ofcombustion.
 7. A method in accordance with claim 6 further including thestep of permitting a fire on a combustion surface in the lower portionto burn upwardly toward the upper portion so that byproducts ofcombustion build on the combustion surface to cause burning fuel to burnat a higher level wherein said higher level has a smaller crosssectional area than said lower portion whereby the byproducts ofcombustion may drop as a unit out of said opening.
 8. A method inaccordance with claim 6 further including the step of causing air toflow through apertures having internal walls arranged in number and sizeto provide adequate combustion as the byproducts of combustion blockholes while the fire burns to higher and higher levels.
 9. A method inaccordance with claim 8 further including the step of moving from fuelfeed setting to fuel feed setting in a controlled serial sequence.
 10. Amethod in accordance with claim 9 further including a delay time betweensettings to avoid a rapid change in rates of fuel feed.
 11. A heatingapparatus including: a burnpot; a combustible air system for providingair to said burnpot at preselected rates; an exhaust system for removinghot gaseous byproducts of combustion; a heat exchange system whereby thehot gaseous byproducts of combustion provide heat to a preselected area;said heat exchange system including a plurality of heat exchanger tubesand means having a plurality of openings, each being shaped and sized tofit over a different heat exchanger tube for scraping the circumferenceof said heat exchange tubes; said burnpot having an openable bottom withat least a first and second position, one of said at least fist andsecond positions being substantially closed so as to enable a body ofcombustible fuel to burn on its upper surface, the other of said atleast first and second positions providing an opening, burnpot side wallportions and atop of said burnpot being shaped so as to permit a solidclinker to drop out of the opening in the openable bottom when theopenable bottom is in the second position.
 12. A burnpot in accordancewith claim 1 having a combustion retention openable burnpot bottom toretain combustion in the burnpot when byproduct of combustion is removedthrough the openable bottom.
 13. A burnpot in accordance with claim 1 inwhich said burnpot side wall portions include apertures through themhaving internal walls, each of said apertures having a correspondingdiameter and internal wall thickness; said thickness being equal to thethickness of the side wall portions; said side wall portions slantingdownwardly toward the openable bottom whereby air entering the side wallportions flows with velocity in the direction of said openable bottom.14. A burnpot within a firebox, said burnpot comprising a source ofcombustion air and an openable bottom with at least a first and secondposition, one of said at least first and second positions beingsubstantially closed so as to enable a body of combustible fuel to burnon its upper surface, the other of said at least first and secondpositions providing an opening, said openable burnpot bottom includingfirst and second bottom walls separated from each other so as to providean airspace between the first and second bottom walls; said first bottomwall having a plurality of first openings extending between the secondbottom wall and an interior of the burnpot, whereby air may pass fromthe airspace into the burnpot and the first bottom wall may hold a solidbyproduct of combustion and at least one second opening between theairspace and said source of combustable air whereby air may pass fromthe source of combustible air and the airspace; and said second bottomwall being without substantial opening whereby the combustible air isprevented from passing into the firebox.
 15. A burnpot comprising anopenable bottom with at least a first and second position, one of saidat least first and second positions being substantially closed so as toenable a body of combustible fuel to burn on its upper surface, theother of said at least first and second positions providing an opening,a slide; said openable bottom resting on said slide; a handle, wherebysaid openable bottom may be moved with the handle to slide between thefirst and second positions and a combustion retention openable burnpotbottom to retain combustion in the burnpot when solid byproduct ofcombustion is removed through the openable bottom; and said combustionretention openable burnpot bottom being located sufficiently close tosaid openable bottom to cause ignition of fuel on said combustionretention openable burnpot bottom from heat rising from said openableburnpot bottom.